Biostimulator having flexible circuit assembly

ABSTRACT

A biostimulator, such as a leadless cardiac pacemaker, having a flexible circuit assembly, is described. The flexible circuit assembly is contained within an electronics compartment between a battery, a housing, and a header assembly of the biostimulator. The flexible circuit assembly includes a flexible substrate that folds into a stacked configuration in which an electrical connector and an electronic component of the flexible circuit assembly are enfolded by the flexible substrate. An aperture is located in a fold region of the flexible substrate to allow a feedthrough pin of the header assembly to pass through the folded structure into electrical contact with the electrical connector. The electronic component can be a processor to control delivery of a pacing impulse through the feedthrough pin to a pacing tip. Other embodiments are also described and claimed.

This application is a continuation of co-pending U.S. Non-Provisionalpatent application Ser. No. 16/687,477, filed on Nov. 18, 2019, andclaims the benefit of priority of U.S. Provisional Patent ApplicationNo. 62/770,088, filed on Nov. 20, 2018, which are incorporated herein byreference in their entirety to provide continuity of disclosure.

FIELD

The present disclosure relates to biostimulators. More specifically, thepresent disclosure relates to leadless biostimulators having flexiblecircuit assemblies.

BACKGROUND

Cardiac pacing by an artificial pacemaker provides an electricalstimulation to the heart when its own natural pacemaker and/orconduction system fails to provide synchronized atrial and ventricularcontractions at rates and intervals sufficient for a patient's health.Such antibradycardial pacing provides relief from symptoms and even lifesupport for hundreds of thousands of patients. Cardiac pacing may alsoprovide electrical overdrive stimulation to suppress or converttachyarrhythmias, again supplying relief from symptoms and preventing orterminating arrhythmias that could lead to sudden cardiac death.

Cardiac pacing by currently available or conventional pacemakers isusually performed by a pulse generator implanted subcutaneously orsub-muscularly in or near a patient's pectoral region. Pulse generatorparameters are usually interrogated and modified by a programming deviceoutside the body, via a loosely-coupled transformer with one inductancewithin the body and another outside, or via electromagnetic radiationwith one antenna within the body and another outside. The generatorusually connects to the proximal end of one or more implanted leads, thedistal end of which contains one or more electrodes for positioningadjacent to the inside or outside wall of a cardiac chamber. The leadshave an insulated electrical conductor or conductors for connecting thepulse generator to electrodes in the heart. Such electrode leadstypically have lengths of 50 to 70 centimeters.

A pulse generator can have electronic circuitry to control cardiacpacing by the leads. For example, the electronic circuitry may include aprinted circuit board. The electronic circuitry can include anintegrated circuit to control the delivery of a pacing impulse from aninterior of a hermetically sealed battery container to an external leadconnection.

SUMMARY

Conventional pacemakers have several drawbacks, including complexconnections between the leads and the pulse generator, and a risk ofinfection and morbidity due to the separate leads and pulse generatorcomponents. Many of the issues associated with conventional pacemakersare resolved by the development of a self-contained and self-sustainablebiostimulator, or so-called leadless biostimulator. The leadlessbiostimulator can be attached to tissue within a dynamic environment,e.g., within a chamber of a beating heart. The attachment of theleadless biostimulator within a target anatomy, however, increases theimportance of miniaturization of the device profile. Accordingly,increasing packaging efficiency of the device, including reducing anoverall volume of the electronic circuitry, is desirable. Furthermore,the colocation of a battery and electronic circuitry, as well as thereduction in the overall volume of the electronic circuitry, canincrease a risk of short-circuiting of the battery or circuitry byconductive residue from a manufacturing process used to fabricated theleadless biostimulator. Accordingly, isolating battery conductors andelectronic circuitry from each other and from surrounding conductivestructures can improve device reliability.

A biostimulator having a flexible circuit assembly, and optionally othercomponents, that are structured and arranged to reduce the likelihood ofshort-circuiting, is provided. In an embodiment, the flexible circuitassembly includes a flexible substrate that has a mounting surface tocarry electrical and electronic components. The flexible substrate canbe folded along a fold region such that a first mounting region and asecond mounting region of the mounting surface face each other. In thefolded, or stacked, configuration, a feedthrough connector and anelectronic component, both of which are on the mounting surface, can beenfolded by the folded flexible substrate. Accordingly, the feedthroughconnector and electronic component can be protected and separated fromsurrounding conductive components, such as a housing or a battery.

The flexible circuit assembly can have an aperture in the fold region.The aperture can be centered on the mounting surface. For example, theaperture can be at a center of the fold region. An aperture axis of theapertures can extend in alignment with, e.g., through or over, thefeedthrough connector. Accordingly, a feedthrough pin of a headerassembly can be inserted through the aperture to connect to thefeedthrough connector. The feedthrough pin can conduct electricalimpulses from the flexible circuit assembly to a target tissue.

In an embodiment, battery connectors are also on the mounting surface.For example, the feedthrough connector and the battery connectors can beon the first mounting region of the mounting surface, and the electroniccomponent, e.g., a processor, can be on the second mounting region ofthe mounting surface. The feedthrough connector and the batteryconnectors can be socket connectors having respective socket axesextending parallel to each other. In an embodiment, the socket axis ofthe feedthrough is laterally between the socket axes of the batteryconnectors. Thus, the electrical pins of the feedthrough and the batterycan support the flexible circuit assembly uniformly at several pointswhen engaged with the respective connectors.

The folded flexible circuit assembly can be folded such that theflexible substrate contacts the adjacent housing and/or battery.Accordingly, the flexible substrate can separate and insulate theelectrical connectors and electronic components from the surroundingstructures. Alternatively, the flexible circuit assembly can beinsulated from the housing and/or the battery by one or more externalcomponents. In an embodiment, an end insulator is located between thebattery and the flexible circuit assembly. The end insulator can be athin-walled planar dielectric film that separates the flexible circuitassembly from the battery. The end insulator can have slots to allow thebattery pins to pass through the end insulator to connect to the batteryconnectors. In an embodiment, the biostimulator includes a wallinsulator located between the housing and the flexible circuit assembly.The wall insulator can be a thin-walled tubular dielectric sleeve thatextends around the flexible circuit assembly to insulate the flexiblecircuit assembly from the housing.

Methods of assembling the biostimulator having the flexible circuitassembly are described. The methods can have operations performed in anorder according to whether the electrical connectors on the flexiblesubstrate are socket connectors or metallized pads. In an embodiment,the methods include using circumferential welds to secure the housing tothe header assembly and the battery. The welds can hermetically seal anelectronics compartment containing the flexible circuit assembly.Accordingly, the biostimulator may include a moisture getter within theelectronics compartment to scavenge residual moisture that couldnegatively impact performance of the electrical connectors or electroniccomponents within the electronics compartment.

The above summary does not include an exhaustive list of all aspects ofthe present invention. It is contemplated that the invention includesall systems and methods that can be practiced from all suitablecombinations of the various aspects summarized above, as well as thosedisclosed in the Detailed Description below and particularly pointed outin the claims filed with the application. Such combinations haveparticular advantages not specifically recited in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe claims that follow. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1A-1B are perspective and exploded views, respectively, of abiostimulator, in accordance with an embodiment.

FIGS. 2A-2B are perspective views of a wall insulator, in accordancewith an embodiment.

FIG. 3 is a perspective view of an inner side of a flexible circuitassembly in a flattened configuration, in accordance with an embodiment.

FIG. 4 is a plan view of an inner side of a flexible circuit assembly,in accordance with an embodiment.

FIG. 5 is a perspective view of an outer side of a flexible circuitassembly in a flattened configuration, in accordance with an embodiment.

FIG. 6 is a plan view of an outer side of a flexible circuit assembly,in accordance with an embodiment.

FIG. 7 is a perspective view of a flexible circuit assembly in a stackedconfiguration, in accordance with an embodiment.

FIG. 8 is a perspective view of an end insulator of a biostimulator, inaccordance with an embodiment.

FIG. 9 is a perspective view of battery pins extending through an endinsulator of a biostimulator, in accordance with an embodiment.

FIG. 10 is a cross-sectional view of an electronics compartment of abiostimulator having a flexible circuit assembly, in accordance with anembodiment.

FIG. 11 is a cross-section electronics compartment of a biostimulatorhaving a flexible circuit assembly, in accordance with an embodiment.

FIG. 12 is a cross-sectional view of a biostimulator having a flexiblecircuit assembly, in accordance with an embodiment.

FIG. 13 is a cross-sectional view of a header assembly connected to aflexible circuit assembly, in accordance with an embodiment.

FIG. 14 is a cross-sectional view of a header assembly and a batteryconnected to a flexible circuit assembly, in accordance with anembodiment.

FIG. 15 is a cross-sectional view of an electronics compartment of abiostimulator containing a wall insulator and a flexible circuitassembly, in accordance with an embodiment.

FIG. 16 is a perspective view of an electronics compartment of abiostimulator containing a wall insulator overmolded on a flexiblecircuit assembly, in accordance with an embodiment.

FIG. 17 is a perspective view of a moisture getter in an electronicscompartment of a biostimulator, in accordance with an embodiment.

FIG. 18 is a perspective view of a moisture getter holder, in accordancewith an embodiment.

FIG. 19 is a perspective view of a moisture getter in an electronicscompartment of a biostimulator, in accordance with an embodiment.

FIG. 20 is a perspective view of a moisture getter holder, in accordancewith an embodiment.

FIG. 21 is a perspective view of a cap insulator, in accordance with anembodiment.

FIG. 22 is a perspective view of an insulating shroud, in accordancewith an embodiment.

DETAILED DESCRIPTION

Embodiments describe a biostimulator, e.g., a leadless cardiacpacemaker, having a flexible circuit assembly that includes a flexiblesubstrate carrying an electronic component and an electrical connector,and an aperture in the flexible substrate to allow a feedthrough pin topass through the flexible substrate to the electrical connector. Theelectronic component can include a processor to control transmission ofa pacing impulse from a battery to a target tissue. The flexible circuitassembly can be folded into a stacked configuration in which theflexible substrate insulates the electronic component from surroundingstructures, e.g., a housing of the biostimulator. Additional components,such as a wall insulator or an end insulator can further insulate theflexible circuit assembly from surrounding structures. The biostimulatormay be used to pace cardiac tissue as described below. Alternatively,the biostimulator may be used in other applications, such as deep brainstimulation. Thus, reference to the biostimulator as being a cardiacpacemaker is not limiting.

In various embodiments, description is made with reference to thefigures. However, certain embodiments may be practiced without one ormore of these specific details, or in combination with other knownmethods and configurations. In the following description, numerousspecific details are set forth, such as specific configurations,dimensions, and processes, in order to provide a thorough understandingof the embodiments. In other instances, well-known processes andmanufacturing techniques have not been described in particular detail inorder to not unnecessarily obscure the description. Reference throughoutthis specification to “one embodiment,” “an embodiment,” or the like,means that a particular feature, structure, configuration, orcharacteristic described is included in at least one embodiment. Thus,the appearance of the phrase “one embodiment,” “an embodiment,” or thelike, in various places throughout this specification are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, configurations, or characteristics maybe combined in any suitable manner in one or more embodiments.

The use of relative terms throughout the description may denote arelative position or direction. For example, “distal” may indicate afirst direction along a longitudinal axis of a biostimulator. Similarly,“proximal” may indicate a second direction opposite to the firstdirection. Such terms are provided to establish relative frames ofreference, however, and are not intended to limit the use or orientationof a biostimulator to a specific configuration described in the variousembodiments below.

In an aspect, a biostimulator is provided. The biostimulator includes apacing tip for delivering a pacing impulse to a target tissue. Thepacing impulse can be controlled and/or transmitted by a flexiblecircuit assembly having an electronic component and an electricalconnector contained within an electronics compartment of thebiostimulator. More particularly, the flexible circuit assembly includesan electronic component and an electrical connector on a mountingsurface of a flexible substrate, which is folded in half within theelectronics compartment. A first mounting region carrying the electroniccomponent and a second mounting region carrying the electrical connectorcan face each other, such that the electronic component and theelectrical connector are sandwiched between and enfolded by the mountingregions. The electronic component and electrical connector can beinsulated from a surrounding structure, e.g., a housing of thebiostimulator, by one or more of the flexible substrate, a wallinsulator, or an end insulator. For example, the wall insulator canseparate the flexible circuit assembly from the housing and the endinsulator can separate the flexible circuit assembly from a battery toreduce a likelihood of electrical short circuiting between conductiveportions of the flexible circuit assembly and either the housing or thebattery.

Referring to FIG. 1A, a perspective view of a biostimulator is shown inaccordance with an embodiment. A biostimulator 100 can be a leadlessbiostimulator, e.g., a leadless cardiac pacemaker. The biostimulator 100can include a distal electrode 104 and a proximal electrode 106 disposedthereon. The electrodes can be integral to a housing 102, or connectedto the housing, e.g., at a distance of less than several centimetersfrom the housing 102. The housing 102 can contain an energy source 107to provide power to the pacing electrodes. The energy source 107 can bea battery, such as a lithium carbon monofluoride (CFx) cell, or a hybridbattery, such as a combined CFx and silver vanadium oxide (SVO/CFx)mixed-chemistry cell. Similarly, the energy source 107 can be anultracapacitor. In an embodiment, the energy source 107 can be an energyharvesting device, such as a piezoelectric device that convertsmechanical strain into electrical current or voltage. The energy source107 can also be an ultrasound transmitter that uses ultrasoundtechnology to transfer energy from an ultrasound subcutaneous pulsegenerator to a receiver-electrode implanted on an endocardial wall.

The biostimulator 100 can have a longitudinal axis 108. The longitudinalaxis 108 can be an axis of symmetry, along which several biostimulatorcomponents are disposed. For example, a header assembly 110 can bemounted on a distal end of the housing 102 along the longitudinal axis108. The header assembly 110 can include an electrical feedthroughassembly including an electrical feedthrough (not shown) and the distalelectrode 104, e.g., a pacing tip. The header assembly 110 can include ahelix mount 112 mounted on the electrical feedthrough assembly aroundthe longitudinal axis 108. In an embodiment, a fixation element 114 ismounted on the helix mount 112 along the longitudinal axis 108. Theassembled components of the biostimulator 100 can provide a distalregion that attaches to a target tissue, e.g., via engagement of thefixation element 114 with the target tissue. The distal region candeliver a pacing impulse to the target tissue, e.g., via the distalelectrode 104 that is held against the target tissue.

Referring to FIG. 1B, an exploded view of a biostimulator having aflexible circuit assembly is shown in accordance with an embodiment. Thehousing 102 can contain an electronics compartment 116. Moreparticularly, the housing 102 can have a housing wall, e.g., acylindrical wall, laterally surrounding the electronics compartment 116.In an embodiment, the housing wall has an inner surface 118 extendingaround the electronics compartment 116 on the longitudinal axis 108. Thehousing wall can include a conductive, biocompatible, inert, andanodically safe material such as titanium, 316L stainless steel, orother similar materials, to laterally enclose the electronicscompartment 116. The electronics compartment 116 can be axially enclosedat a proximal end by the battery. More particularly, a distal surface orface of the battery can define the proximal end of the electronicscompartment 116. The electronics component 116 can be axially enclosedat a distal end by the header assembly 110. More particularly, aproximal surface of the header assembly 110 can define the distal end ofthe electronics compartment 116. The housing 102 can be attached, e.g.,welded, to the header assembly 110 and the battery 107. Accordingly, theelectronics compartment 116 can be contained between the battery, theinner surface 118 of the housing 102, and the header assembly 110.

In an embodiment, a flexible circuit assembly 120 is contained withinthe electronics compartment 116. The flexible circuit assembly 120 caninclude a flexible substrate having one or more electronic componentsmounted on a flexible substrate. For example, the flexible circuitassembly 120 can include one or more passive electronic components,e.g., capacitors, and one or more active electronic components, e.g.,processors. The electronic components can be interconnected byelectrical traces, vias, or other electrical connectors. In anembodiment, the electronics assembly includes one or more electricalconnectors, e.g., socket and pin connectors or metallized contact pads,to connect to the battery and the electrical feedthrough assembly. Forexample, the electrical connector can be a socket connector or ametallized pad to receive and/or connect to an electrode pin or aterminal pin, as described below.

The electrical connectors of the flexible circuit assembly 120 can beaccidentally short-circuited to other conductive components of thebiostimulator 100 such as the housing 102 or battery 107. To reduce thelikelihood of such an event, the biostimulator 100 may incorporatecomponents to electrically insulate and/or protect the flexible circuitassembly components from short-circuiting. For example, thebiostimulator 100 can include an end insulator 122. The end insulator122 can include a planar structure to form a wall between the flexiblecircuit assembly 120 and the energy source 107. As described below, theend insulator 122 can separate the battery, and more particularly anenclosure of the battery, from the flexible circuit assembly 120. Thebiostimulator 100 may also include a wall insulator 124. As describedbelow, the wall insulator 124 can separate the flexible circuit assembly120 from the inner surface 118 of the housing 102. It will beappreciated that the flexible substrate of the flexible circuit assembly120 may provide sufficient insulation and separation from the housing102 and the battery, and thus, the end insulator 122 and the wallinsulator 124 are optional. The insulating components are nonethelessdescribed as being part of the embodiments below.

Referring to FIG. 2A, a perspective view of a wall insulator is shown inaccordance with an embodiment. The flexible circuit assembly 120 can beseparated from the housing 102 to reduce the likelihood ofshort-circuiting between the electronic components on the flexiblecircuit assembly 120 and the housing 102, during both manufacturing anduse of the biostimulator 100. The wall insulator 124 can be a tubularcomponent. For example, the wall insulator 124 can have the form of acylindrical tube. The cylindrical tube can include a wall outer surface202 and a wall interior surface 204, both of which may be cylindrical,extending between a distal wall end 206 and a proximal wall end 208. Thetubular structure of the wall insulator 124 allows the insulator to bemounted over the flexible circuit assembly 120 to circumferentiallyenclose the flexible circuit assembly 120. More particularly, the wallinsulator 124 can extend around the flexible circuit assembly 120 withinthe electronics compartment 116 of the biostimulator 100. Accordingly,the wall insulator 124 can separate the flexible circuit assembly 120from the inner wall 118 of the housing 102.

In an embodiment, a cross-sectional profile of the wall insulator 124,taken along a plane extending perpendicular to the longitudinal axis108, is circular. More particularly, a profile of the wall outer surface202 and the wall interior surface 204 may be circular. Alternatively,the cross-sectional profile of the wall insulator 124 can be polygonal,elliptical, or another shape.

In an embodiment, the wall insulator 124 is formed from a thindielectric film. For example, the wall insulator 124 can be a thincylindrical insulating sleeve formed from any material having gooddielectric properties (electrically insulating). As described below, thewall insulator 124 may fit within the electronics compartment 116between the housing 102 and the flexible circuit assembly 120, and thus,it may be advantageous to form the wall insulator 124 from a materialcapable of forming a thin wall having tight tolerances. The wallinsulator 124 may also benefit from having good hoop strength.Accordingly, the wall insulator 124 may be formed frompolytetrafluoroethylene or polyimide because those materials have thedesired characteristics.

Referring to FIG. 2B, a perspective view of a wall insulator is shown inaccordance with an embodiment. The wall insulator 124 may be anexpandable sleeve. In an embodiment, the wall insulator 24 has acorrugated tubular structure. For example, the tubular structure canhave several longitudinal folds 210 extending in the longitudinaldirection 318 between the distal wall end 206 and the proximal wall end208. The folds 210 or corrugations impart a non-circular profile to thewall outer surface 202 and the wall interior surface 204. Moreparticularly, the tubular surfaces of the wall insulator 124 may definea thin wall that undulates in a circumferential direction around thelongitudinal axis 108.

The longitudinal folds 210 of the wall insulator 124 allow the insulatorto expand and contract radially. For example, an inward radial forceapplied to the wall outer surface 202 can cause an angle between theundulating surfaces to decrease, thereby reducing a diameter of the wallinsulator 124. By contrast, an outward radial force applied to the wallinterior surface 204 can cause the angle between the undulating surfacesto increase, thereby increasing a diameter of the wall insulator 124.The expandable/collapsible tubular structure can allow the wallinsulator 124 to conform to adjacent components. For example, the wallinsulator 124 can be placed within the housing 102, and may collapsesuch that the wall outer surface 202 contacts and fits within the innersurface 118 of the housing 102. Similarly, the wall insulator 124 can beplaced over the flexible circuit assembly 120, and may expand such thatthe wall interior surface 204 contacts an exterior of the flexiblecircuit assembly 120. The wall insulator 124 may therefore adapt to theadjacent structures to provide a close fit that uses minimal spacebetween the housing 102 and the flexible circuit assembly 120.

As mentioned above, the wall insulator 124 can be formed from anyelectrically insulating material. In an embodiment, the wall insulator124 is formed from a heat-shrinkable material. For example, the wallinsulator 124 may be a heat-shrinkable tube formed from a polyolefin orfluoropolymer material. In such case, heat may be applied to the wallinsulator 124 to cause it to shrink onto and conform to the flexiblecircuit assembly 120. The heat-shrinkable tubing, when in the shrunkstate, may wrap around and isolate the electronic components of theflexible circuit assembly 120 from surrounding structures, such as thehousing 102.

Referring to FIG. 3, a perspective view of an inner side of a flexiblecircuit assembly in a flattened configuration is shown in accordancewith an embodiment. The flexible circuit assembly 120 for thebiostimulator 100 can have a flattened configuration 302. In anembodiment, the flexible circuit assembly 120 includes a flexiblesubstrate 304. For example, the flexible substrate 304 can include aflexible polymer film, such as a film including polyester, polyethylenenaphthalate, polyetherimide, fluoropolymers, and combinations thereof.In an embodiment, flexible substrate 304 is a polyimide substrate thatcan be resiliently bent or folded.

The flexible substrate 304 can include several mounting surfaces facingin opposite directions, e.g., a top surface (FIG. 3) and a bottomsurface (FIG. 5). The top surface, which is shown in FIG. 3, may also bereferred to as an inner side of the flexible circuit assembly 120because the top surface faces an internal gap of a folded structure whenthe flexible circuit assembly 120 is folded from the flattenedconfiguration 302 into a stacked configuration, as described below. Inan embodiment, the mounting surfaces include a mounting surface 306carrying one or more electrical connectors 308 and one or moreelectronic components 310. The mounting surface 306 can be a planarsurface in the flattened configuration 302, and can have several regionsdesignated according to their function.

In an embodiment, the mounting surface 306 of flexible substrate 304includes a first mounting region 312 and a second mounting region 314.One or more electrical connectors 308 and/or electronic components 310can be mounted on first mounting region 312. Similarly, one or moreelectrical connectors 308 and/or electronic components 310 can bemounted on second mounting region 314. In an embodiment, only one of themounting regions carries electrical connector(s) 308.

The mounting surface 306 can include a fold region 316 between the firstmounting region 312 and the second mounting region 314. For example,each mounting region can have a region boundary defined by longitudinalboundaries separated in a longitudinal direction 318, and lateralboundaries separated in a lateral direction 320. The fold region 316 canbe a segment of the flexible substrate 304 extending across the mountingsurface 306 in the lateral direction 320 from a first lateral edge 322of the flexible substrate 304 to a second lateral edge 324 of theflexible substrate 304. The flexible substrate 304 is configured to foldalong the fold region 316 into a stacked configuration (FIG. 7) suchthat the first mounting region 312 of the inner surface faces the secondmounting region 314 of the inner surface in a transverse direction 325orthogonal to the longitudinal direction 318 and the lateral direction320.

In an embodiment, one or more electrical traces 350 extend over the foldregion 316. More particularly, the electrical traces 350 can extend fromthe first mounting region 312 to the second mounting region 314 acrossthe fold region 316. The electrical traces 350 can be disposed on, orembedded within, the flexible substrate 304. The electrical traces 350can electrically connect a first component, e.g., a socket connector,mounted on the first mounting region 312 to a second component, e.g., aprocessor, mounted on the second mounting region 314. Accordingly, theelectrical traces 350 can fulfill an electrical communication function.

The electrical traces 350 may also fulfill a mechanical function. In anembodiment, the electrical traces 350 act as strain reliefs todistribute stress evenly over the fold region 316. The electrical traces350 can have a thickness and/or width to prevent kinking in the foldregion 316. Furthermore, the electrical traces 350 may be formed from aductile material that resists kinking. For example, the electricaltraces 350 can be copper alloy traces having predetermined dimensionsand traces per inch density, which are embedded in flexible substrate304 within the fold region 316 such that, when the flexible circuitassembly is folded into a stacked configuration (FIG. 7), the foldregion 316 extends along an arcuate path, e.g., a smooth curve, ratherthan kinking or bending abruptly.

In an embodiment, the flexible substrate 304 includes an aperture 326extending through the flexible substrate 304. More particularly, theaperture 326 can be a hole or a slot extending from the inner side ofthe flexible substrate 304 to the outer side on an opposite side of theflexible substrate 304. The aperture 326 can be in the fold region 316,and can have an aperture axis 352. The aperture axis 352 may be definedwith respect to an edge of the aperture 326. For example, an apertureplane may contain the edge that extends around the aperture 326, and theaperture axis 352 may extend perpendicular to the aperture plane.Accordingly, the aperture axis 352 may be parallel to the transversedirection 325 when the flexible circuit assembly 120 is in the flattenedconfiguration 302, and by contrast, the aperture axis 352 may beparallel to the longitudinal direction 108 when the flexible circuitassembly 120 is in the stacked configuration. In the stackedconfiguration, the aperture axis 352 can be parallel to the longitudinalaxis 108, as described below.

In an embodiment, the aperture 326 can be centered on the mountingsurface 306. For example, the fold region 316 can be spaced equallybetween a first longitudinal edge 330 and a second longitudinal edge 332of flexible substrate 304. Accordingly, the aperture 326 in the foldregion 316 can be longitudinally centered between the first longitudinaledge 330 and the second longitudinal edge 332. Similarly, the aperture326 in the fold region 316 can be laterally centered between the firstlateral edge 322 and the second lateral edge 324. Thus, the aperture 326can be at a center of the mounting surface 306.

Referring to FIG. 4, a plan view of an inner side of a flexible circuitassembly is shown in accordance with an embodiment. The electricalconnectors 308 on the mounting surface 306 can include a feedthroughconnector 402 mounted on the first mounting region 312. The feedthroughconnector 402 can be one of several types of electrical connectors 308.For example, the feedthrough connector 402 can be a socket connector(FIGS. 3-7 and 10-12) or a metallized pad (FIGS. 13-15). The feedthroughconnector 402 can be configured to receive an electrical pin fromanother component of the biostimulator 100. For example, the feedthroughconnector 402 can receive and/or attach to a feedthrough pin of theheader assembly 110 that transmits a pacing impulse from the flexiblecircuit assembly 120 to the pacing tip of the biostimulator 100.

In an embodiment, the feedthrough connector 402 is a socket connectorand has a socket axis 404 passing through a lumen of the socketconnector. The socket axis 404 can extend in the longitudinal direction318. In an embodiment, the socket axis 404 is laterally aligned with acenter 406 of the mounting surface 306. Accordingly, the socket axis 404can be transversely aligned with the aperture 326.

As described above, the aperture 326 can be centered on the mountingsurface 306. The center 406 can be aligned with the socket axis 404 thatis equidistantly spaced between the first lateral edge 322 and thesecond lateral edge 324. Similarly, the center 406 can be aligned with amidline 408 of the mounting surface 306, which extends orthogonal to thesocket axis 404. The midline 408 can be equidistantly spaced between thefirst longitudinal edge 330 and the second longitudinal edge 332 of theflexible substrate 304.

The flexible circuit assembly 120 can include several electricalconnectors 308 on the mounting surface 306. For example, one or morebattery connectors 410 can be on the mounting surface 306. The batteryconnectors 410 can be one of several types of electrical connectors 308.For example, the battery connectors 410 can be socket connectors (FIGS.3-7 and 10-12) or metallized pads (FIGS. 13-15). The battery connectors410 may be configured to receive and/or attach to electrical pins ofanother component of the biostimulator 100. For example, batteryconnectors 410 can receive battery pins of the energy source 107 totransmit power from the battery to the flexible circuit assembly 120.The battery pins can be a positive terminal post and a negative terminalpost of the battery. Accordingly, electrical power can be input to theflexible circuit assembly 120 via the battery connectors 410, andelectrical power can be output from the flexible circuit assembly 120via the feedthrough connector 402.

Each battery connector 410 can be a socket connector having a respectivesocket axis 404. The respective socket axes 404 of the batteryconnectors 410 can extend parallel to the socket axis 404 of thefeedthrough connector 402. In an embodiment, the socket axes 404 of theflexible circuit assembly 120 extend in the longitudinal direction 318of the biostimulator 100. For example, the socket axes can be parallelto the longitudinal axis 108 when the flexible circuit assembly 120 iscontained within the electronics compartment 116 of the housing 102.Notably, the socket axes 404 may also be parallel to the aperture axis352 in such a configuration. Accordingly, as described further below,when the flexible circuit assembly 120 is folded about the fold region316 to mount the flexible circuit assembly 120 within the electronicscompartment 116, the reference geometry of the socket axes 404 extendlongitudinally through the fold region 316 of the mounting surface 306.More particularly, the socket axes 404 can extend parallel to mountingsurface 306 over the first and second mounting regions, and orthogonalto the mounting surface 306 at the locations where the axes intersectthe fold region 316.

The electrical connectors 308 of the flexible circuit assembly 120 maybe located to stably support the flexible circuit assembly 120 on theelectrical pins that the socket connectors receive. In an embodiment,the external pins, e.g., the feedthrough pin and the battery pins, canbe evenly loaded by the electrical connectors 308 on the mountingsurface 306. For example, the socket axis 404 of the feedthroughconnector 402 can be located between the socket axes 404 of the batteryconnectors 410. More particularly, the socket axis 404 of thefeedthrough connector 402 may be laterally between, relative to thelateral direction 320, the socket axes of the battery connectors 410. Inan embodiment, the socket axis 404 of the feedthrough connector 402 isequidistantly spaced between the socket axes 404 of the batteryconnectors 410. Accordingly, the mechanical connections formed betweenthe electrical connectors 308 of the flexible circuit assembly 120 andthe external biostimulator components can be symmetrically locatedacross the first mounting region 312.

Still referring to FIG. 4, in addition to having several electricalconnectors 308, flexible substrate 304 can carry one or more electroniccomponents 310 on the mounting surface 306. In an embodiment, one ormore of the electronic components 310 is on the second mounting region314 of the mounting surface 306. For example, the electronic component310 on the second mounting region 314 can include an active electroniccomponent 420, such as a semiconductor device. The electronic component310 on the second mounting region 314 can include one or more processors422. More particularly, the electronic component 310 can include anintegrated circuit, such as an application-specific integrated circuit,having microprocessors and/or memory blocks designed to run in thebiostimulator 100 to provide cardiac pacing. In an embodiment, the oneor more processors 422 are configured to execute instructions stored ina non-transitory computer readable media to cause the biostimulator 100to perform various operations, including but not limited to generatingand transmitting the pacing impulse to the target tissue.

In addition to active components 420, flexible circuit assembly 120 caninclude one or more passive electronic components 424 mounted on themounting surface 306. For example, the passive electronic components 424can include one or more capacitors. The capacitors can be polymer orceramic capacitors, by way of example.

In an embodiment, a shear stress applied to the electronic components310 and/or electrical connectors 308 mounted on the mounting surface 306can be mitigated by an epoxy underfill. More particularly, the epoxyunderfill can be disposed between the mounting surface 306 and theelectrical/electronic components 310 during manufacturing. The epoxyunderfill can be a layer of epoxy adhesive that is flowed between theelectrical/electronic components 310 and the mounting surface 306 afterthe electrical/electronic components 310 are mounted on the mountingsurface 306. For example, surface mount technology, e.g., reflowedsolder balls, can be used to electrically and/or physically connect thecomponents to electrical contacts on the mounting surface 306, and a gapcan remain between the components and the surface after componentattachment. The epoxy adhesive can be flowed into the gap to furtherstabilize and secure the components on the mounting surface 306. In anembodiment, the underfill layer can have a thickness of 0.008 inch to0.1 inch, e.g., 0.010 inch.

Referring to FIG. 5, a perspective view of an outer side of a flexiblecircuit assembly in a flattened configuration is shown in accordancewith an embodiment. In the flattened configuration 302, a second surfaceof the flexible substrate 304 can have a respective mounting surface 306divided into regions as described above. For example, the mountingsurface 306 can have the first mounting region 312 and the secondmounting region 314. The second surface may be referred to as the outerside of the flexible circuit assembly 120 because the second surface mayface outwardly toward the housing 102 when the flexible substrate 304 isfolded from the flattened configuration 302 into the stackedconfiguration as described below.

Referring to FIG. 6, a plan view of an outer side of a flexible circuitassembly is shown in accordance with an embodiment. The mounting regionsof the bottom surface can carry one or more electronic components 310,which can be active components 420 or passive components 424. Forexample, the electronic components 310 can include diodes, transistors,capacitors, etc. In an embodiment, the mounting regions of the outerside carry one or more sensors 602. The sensor 602(s) can detecttemperature, acceleration, etc. For example, a micro electromechanicalsystem (MEMS) sensor can be mounted on the flexible substrate 304. TheMEMS sensor can be a giant magnetoresistance (GMR) sensor, by way ofexample. Similarly, an electronic oscillator circuit 604 can be mountedon the flexible substrate 304. It will be appreciated that theelectronic components 310 described above are provided by way ofexample, and that other electronic components 310 may be mounted onflexible substrate 304. More particularly, surface-mount technology canbe used to produce flexible circuit assembly 120 having componentsmounted or placed directly on the flexible substrate 304. Electricalconnections between the individual components may be made using traces,electrical vias, pins, contacts, etc. For example, as described above,the electrical traces 350 can extend over the fold region 316 fromcomponents on the first mounting region 312 to components on the secondmounting region 314. The electrical traces 350 can be exposed or buried,e.g., laminated. Accordingly, a two-sided flexible circuit assembly 120having a centrally-located aperture 326 can be provided for use in thebiostimulator 100.

Referring to FIG. 7, a perspective view of a flexible circuit assemblyin a stacked configuration is shown in accordance with an embodiment.The flexible circuit assembly 120 can be folded along the fold region316 into a stacked configuration 702. In the stacked configuration 702,the socket axis 404 of the feedthrough connector 402 can extend throughthe aperture 326 in the longitudinal direction 318 (FIG. 11). Similarly,the aperture axis 352 can extend between the first mounting region 312and the second mounting region 314 in the stacked configuration 702. Forexample, the socket axis 404 can extend through the aperture 326parallel to the longitudinal axis 108, and the aperture axis 352 canextend through the aperture 326 in alignment with the feedthroughconnector 402. More particularly, the aperture axis 352 can extendthrough a pin port of the socket connector that receives an externalpin. Similarly, the socket axes 404 of the battery connectors 410 canextend in the longitudinal direction 318 opposite to the socket axis 404of the feedthrough connector 402 to emerge from a protective gap 704defined between the first longitudinal edge 330 and the secondlongitudinal edge 332. The aperture axis 352 can extend between themounting regions to emerge from the protective gap 704 laterally betweenthe socket axes of the battery connectors 410.

The protective gap 704 can be a space enfolded by the flexible substratebetween the first mounting region 312 and the second mounting region314. In the stacked configuration 702, the first mounting region 312faces the second mounting region 314 across the protective gap 704.Accordingly, the electrical connectors 308 and/or electronic components310 mounted on the inner side of the flexible circuit assembly 120 arecontained within the protective gap 704 in the stacked configuration702. For example, the feedthrough connector 402 and the electroniccomponent 310 can be stacked on each other, and thus, are in the stackedconfiguration 702. The flexible substrate 304 can wrap around theelectronic components 310 and the electrical connectors 308. Thecomponents are therefore enclosed within the protective gap 704, andthus, a likelihood that conductive debris will form a short-circuitbetween the components and a location outside of the protective gap 704is reduced. The likelihood can be further reduced by closing off theends of the protective gap 704, e.g., where the protective gap 704 opensto the surrounding environment in the longitudinal direction 318 or thelateral direction 320.

Referring to FIG. 8, a perspective view of an end insulator of abiostimulator is shown in accordance with an embodiment. The endinsulator 122 can be placed between the openings of the protective gap704 and the surrounding environment. In an embodiment, the end insulator122 is planar, e.g., has a flat distal end face 806 and a flat proximalend face (hidden from view). More particularly, the end insulator 122can be a thin, flat, disc-shaped insulator. The end insulator 122 caninclude a thin dielectric film formed from a dielectric material, e.g.,polyimide. The end insulator 122 may include an outer edge 802 defininga profile of the end insulator 122. For example, the profile of the endinsulator 122 can be circular, as shown in FIG. 8. Alternatively, theend insulator 122 can have a polygonal, elliptical, or other profileshape.

In an embodiment, the end insulator 122 includes one or more slots 804extending through the thin wall of the insulator. For example, the endinsulator 122 can include several slots 804, each having a respectivesize and profile. As shown, the several slots 804 can include a pair ofslots 804, each having a circular profile. The slots may be elliptical,polygonal, etc. A dimension of the profiles, e.g., a diameter of thecircles, however, may differ. For example a first slot 804 of the endinsulator 122 may have a larger diameter than a second slot 804 of theend insulator 122. Alternatively, the slots 804 may have a same size andshape. For example, the slots 804 of the end insulator 122 may both beelliptical and have a same length and width.

Referring to FIG. 9, a perspective view of battery pins extendingthrough an end insulator of a biostimulator is shown in accordance withan embodiment. The end insulator 122 may be configured to cover a faceof the energy source 107 while allowing the terminal posts of thebattery to pass through the end insulator 122 into electrical contactwith the electrical connectors 308 of the flexible circuit assembly 120.In an embodiment, the battery includes one or more battery pins 902,which can be the positive and negative terminal posts of the battery.The battery pins 902 can extend from a distal face 904 of the battery inthe longitudinal direction 318, e.g., parallel to the longitudinal axis108. More particularly, the battery pins 902 can have respective pinaxes 902, and the pin axes 902 can extend parallel to the aperture axis352 when the flexible circuit assembly 120 is in the stackedconfiguration 702. During assembly of the biostimulator 100, the batterypins 902 can be inserted through respective slots 804 of the endinsulator 122. Accordingly, the end insulator 122 can be laid on thedistal face 904 of the battery to insulate the distal face 904 and theactive terminal pin from conductive debris that is on an opposite sideof the end insulator 122, e.g., toward the distal tips of the batterypins 902.

In an embodiment, the battery pins 902 include a positive pin 906 and anegative pin 908. Each of the battery pin 902 outer diameter sizes andlengths can be varied to allow for a single, correct placement of thepins into their respective battery connectors 410 on the flexiblecircuit assembly 120. These differently sized battery pins 902 canprevent the incorrect insertion into the battery connectors 410, whichcould cause latent and catastrophic failures within the flexible circuitassembly 120. For example, the positive pin 906 can have a largerdiameter than the negative pin 908, and accordingly, the batteryconnector 410 that receives the negative pin 908 may have a socket thatincludes a socket port that is too small to receive the positive pin906. Accordingly, the pin sizes ensure that the battery will becorrectly oriented with respect to the flexible circuit assembly 120when the components are assembled.

In addition to controlling pin orientation, the pin size canpreferentially direct force to one of the battery pins 902. For example,the positive pin 906 may interface with the glass-to-metal feedthroughof the battery, and thus, it may be advantageous to steer deflectionforces toward the negative pin 908, which interfaces with the batterymetal header. More particularly, the glass-to-metal feedthrough may bemore fragile than the battery metal header, and thus, it may beadvantageous to apply strain to the negative pin 908, which transmitsforces to the battery metal header, rather than to the positive pin 906,which transmits forces to the glass-to-metal feedthrough. For example,off-axis assembly forces, e.g., generated during manual assembly, can bedirected or focused on the negative pin 908 to protect the positive pin906 and glass-to-metal feedthrough seal. This preferential direction ofthe off-axis assembly forces can occur for several reasons. First, thenegative pin 908 may be longer than the positive pin 906, and thus, thenegative pin 908 may be contacted by an assembler or an externalcomponent before the positive pin 906 is contacted. Second, negative pin908 may be narrower and/or longer than the positive pin 906, and thus,may deflect more readily under the off-axis assembly forces.Accordingly, deflection and stresses can be directed toward the negativepin 908 to reduce the likelihood of damage to the glass-metal seal.

Referring to FIG. 10, a cutaway view of an electronics compartment of abiostimulator having a flexible circuit assembly is shown in accordancewith an embodiment. Each of the battery pins 902 of the battery can beconnected to and/or mounted on or inside of respective batteryconnectors 410. For example, in the case of socket connectors, eachbattery pin 902 can be inserted through respective slots 804 in the endinsulator 122, and can extend through the slot 804 into the socket ofthe respective battery connector 410. Similarly, in the case ofmetallized pads, each battery pin 902 can extend through respectiveslots 804 in the end insulator 122, and can attach to metallized pads ofthe flexible circuit assembly 120. As such, in the assembled state, theend insulator 122 can be between the distal face 904 of the battery andthe flexible circuit assembly 120 when the battery pins 902 areconnected to respective battery connectors 410. Accordingly, theflexible circuit assembly 120 can include several battery connectors 410mounted on or attached to respective battery pins 902 of the battery,and the conductive components of the flexible circuit assembly 120 canbe isolated from the distal face 904 of the battery by the end insulator122.

Still referring to FIG. 10, the housing 102 can be mounted over the wallinsulator 124 and onto the battery to contain the flexible circuitassembly 120 within the electronics compartment 116. More particularly,the inner surface 118 of the housing 102 can extend around the flexiblecircuit assembly 120 to laterally surround the flexible circuit assembly120. In an embodiment, the header assembly 110 can be mounted on thehousing 102 to contain the electronics compartment 116 within thebiostimulator 100.

The header assembly 110 can include several subcomponents. For example,the header assembly 110 may include a flange 1004 having a mounting wallto receive a helix mount 112. In an embodiment, the flange 1004 isformed from titanium. The flange 1004 can be mounted on the housing 102and connected to the housing 102 by a hermetic seal, e.g., by a weld.For example, the hermetic weld can be formed circumferentially around aseam between a proximal end of the flange 1004 and a distal end of thehousing 102. In an embodiment, the helix mount 112 is mounted on theflange 1004 by a threaded connection. The flange 1004 can have anexternal thread that mates with an internal thread of the helix mount112. Accordingly, the helix mount 112 can be screwed onto the mountingwall of the flange 1004. Alternatively, the helix mount 112 can be pressfit onto the mounting wall, the helix mount 112 can be bonded to themounting wall by a thermal or adhesive bond, or the helix mount 112 andthe electrical feedthrough assembly can be joined in another manner,such as swaging. Accordingly, the electronics compartment 116 can becontained between the battery, the inner surface 118 of the housing 102,and the header assembly 110.

In an embodiment, the header assembly 110 includes the fixation element114, e.g., a helix. The helix can extend distally from the helix mount112 about the longitudinal axis 108. For example, the helix can revolveabout the longitudinal axis 108. The helix can include a spiral wire,formed by coiling or cut from a wall of a tubing, which extends in arotational direction around the longitudinal axis 108. For example, thehelix can revolve in a right-handed direction about the longitudinalaxis 108.

The helix can be suitable for attaching the biostimulator 100 to tissue,such as heart tissue. For example, in the case of a right-handed spiraldirection, the biostimulator 100 can be advanced into contact with atarget tissue, and the biostimulator 100 can then be rotated in theright-handed direction to screw the helix into the tissue.

Referring to FIG. 11, a cross-sectional view of a biostimulator having aflexible circuit is shown in accordance with an embodiment. The headerassembly 110 can include a feedthrough 1102 to transmit the pacingimpulses from the flexible circuit assembly 120 into the target tissue.For example, the feedthrough 1102 can have a feedthrough pin 1104. Thefeedthrough pin 1104 can extend proximally through the flange 1004 intothe electronics compartment 116 to engage the feedthrough connector 402.More particularly, the feedthrough pin 1104 can be inserted through theaperture 326 in the fold region 316 of the flexible substrate 304 andinto the feedthrough connector 402. Accordingly, the feedthrough pin1104 can be mechanically and electrically connected to the feedthroughconnector 402 between the first mounting region 312 and the secondmounting region 314 of the mounting surface 306.

The feedthrough 1102 can also include an electrode tip 1106, which canbe electrically continuous with the feedthrough pin 1104. Accordingly,when the fixation element 114 is engaged with the target tissue, theelectrode tip 1106 can be held against the tissue, and thus, the pacingimpulse can be delivered from the feedthrough connector 402 into thefeedthrough pin 1104 and through the electrode tip 1106 into the targettissue.

As the flexible circuit assembly 120 can provide power to thefeedthrough 1102 via feedthrough connector 402, so can the flexiblecircuit assembly 120 receive power from the battery through the batteryconnectors 410. More particularly, the battery pins 902 can extendthrough the slots 804 of the end insulator 122 into the electronicscompartment 116. The battery pins 902 can have respective pin axes 910,and each of the pin axes 910 can be parallel to the aperture axis 352.The battery pins 902 can mechanically and electrically connect to thebattery connectors 410. Accordingly, the electrical connectors 308 ofthe flexible circuit assembly 120 can form secure and stable connectionsto the battery pins 902 and the feedthrough pin 1104 to allow electricaltransmission of power with a reduced likelihood of short-circuiting theelectrical connectors 308 to another component of the biostimulator 100.

Referring to FIG. 12, a cross-sectional view of a biostimulator having aflexible circuit assembly is shown in accordance with an embodiment. Inaddition to the protective function of the folded flexible circuitassembly 120, the stacked configuration 702 allows the electronicscompartment 116 to be efficiently occupied by the circuit components.For example, stacking the electrical connectors 308 and the electroniccomponents 310 allows more circuitry per unit length in the longitudinaldirection 318 within the electronics compartment 116. In an embodiment,the stacked flexible circuit assembly 120 can be circumferentiallyenclosed by the wall insulator 124 that can electrically isolate theassembly from the inner surface 118 of the housing 102. As shown, theend insulator 122 can have the outer edge 802 having a circular profile,and the inner surface 118 of the housing 102 and/or the interior surface204 of the wall insulator 124 can have the same circular profile. Thecircular profile is provided by way of example only, and the innersurface 118 and/or the outer edge 802 may have an alternative profile,such as a polygonal or elliptical profile. The profiles of the innersurface 118 (or interior surface 204) and the outer edge 802 can besimilarly sized, e.g., can have a same diameter within a tolerance of+/−10%, to allow for the wall insulator 124, and the end insulator 122to fully encompass the flexible circuit assembly 120 and its componentswhile still fitting inside the housing 102.

The biostimulator 100 can include components to further insulate andprotect the flexible circuit assembly components. In an embodiment, thebiostimulator 100 includes a foam tape 1202 between the electricalconnector(s) 308 and the electronic component 310, which are mountedwithin the protective gap 704. For example, the foam tape 1202 can be astrip of tape having a perimeter that is the same size as a perimeter ofthe first mounting region 312 and/or the second mounting region 314. Thefoam tape 1202 can be single-sided or double-sided tape, and can bemounted over the first mounting region 312 or the second mounting region314 when the flexible circuit assembly 120 is in the flattenedconfiguration 302. When the flexible circuit assembly 120 is folded intothe stacked configuration 702, a first side of the tape can face thefirst mounting region 312 and a second side of the tape can face thesecond mounting region 314. The foam tape 1202 can adhere to theelectronic components 310 and/or the electrical connectors 308 on theinterior side of the folded substrate to retain the flexible circuitassembly 120 in the folded configuration until the socket connectors aremounted on the plug connectors of the biostimulator 100. Furthermore,the foam tape 1202 can be formed from an insulating foam material, andthus, can reduce a likelihood of electrical contact between electricalcomponents on the first mounting region 312 and electrical components onthe second mounting region 314.

In an embodiment, the flexible substrate 304 of the flexible circuitassembly 120 insulates and stabilizes the electronic components 310 andthe electrical connectors 308 relative to the housing 102. As describedabove, the flexible substrate 304 can be a thin dielectric film, e.g., astrip of flexible polyimide. The flexible substrate 304 can have aperipheral edge 1204 that extends around the mounting surface 306 of theflexible circuit assembly 120, e.g., along the lateral and longitudinaledges of the mounting regions and the fold region 316. Moreparticularly, the peripheral edge 1204 can include the lateral andlongitudinal edges of the mounting regions and the fold region 316. Atleast a portion of the peripheral edge 1204 can be in contact with thewall insulator 124 along the inside of the housing 102. For example,when the flexible circuit assembly 120 is in the stacked configuration702 and enclosed within the electronics compartment 116, the mountingregions can move away from each other, e.g., if the foam tape 1202 losesadherence to one side of the substrate, and as the substrate halves moveoutward, the peripheral edge 1204 can contact the interior surface ofthe wall insulator 124. The wall insulator can constrain the outwardmovement of the flexible substrate 304, and a portion of the peripheraledge 1204, e.g., the first lateral edge 322 or the second lateral edge324, can contact the wall insulator 124, on an opposite side of theinsulator wall from the housing 102. The portion of the flexible circuitassembly 120 that contacts the wall insulator 124, e.g., the firstlateral edge 322 or the second lateral edge 324 of the flexiblesubstrate 304, can be formed from an insulating material. Moreparticularly, the peripheral edge 1204 of the flexible substrate 304 canhave no conductive traces or conductive components thereon, such thatcontact between the flexible circuit assembly 120 and the interiorsurface of the wall insulator 124 is not in electrical contact.

The physical, non-electrical, contact between the wall insulator 124 andthe flexible circuit assembly 120 can stabilize the flexible circuitassembly 120 within the electronics compartment 116. When the peripheraledge 1204 of the flexible substrate 304 presses against the interiorsurface 204 of the wall insulator 124, the wall insulator 124 and thehousing 102 that surrounds the wall insulator 124, act essentially as anexternal frame for the flexible circuit assembly 120. Impacts,vibrations, or other forces acting on the flexible circuit assembly 120can be counteracted by the wall insulator 124 and the housing 102.Accordingly, physical contact between the wall insulator 124 and theflexible circuit assembly 120 can limit deflections and loading of theflexible circuit assembly 120. More particularly, stresses applied tothe connector pins, e.g., the feedthrough pin 1104 and/or the batterypins 902, by the electrical connectors 308 can be limited by theexternal support provided by the wall insulator 124 and the housing 102.Furthermore, the external frame provided by the wall insulator 124 andthe housing 102 requires fewer parts and is more space-efficient thanwould be the case if a separate external framework was used to supportthe flexible circuit assembly 120 within the electronics compartment116. Accordingly, supporting a length of the peripheral edge 1204 of theflexible circuit assembly 120 by the wall insulator 124 and the housing102 along an insulated (non-conductive) portion of the flexiblesubstrate 304 provides for a robust and compact biostimulator 100.

The wall insulator and the end insulator embodiments described above areprovided by way of example, and not limitation. For example, in anembodiment, the wall insulator 124 may be replaced by an insulatingcoating applied to the inner surface 118 of the housing 102. Theinsulating coating can be a conformal coating of parylene, for example,and can insulate the metallic housing 102 material from the flexiblecircuit assembly 120. Accordingly, the wall insulator 124 may be aseparate component or integrally formed with the housing 102.

Referring to FIG. 21, a perspective view of a cap insulator is shown inaccordance with an embodiment. The wall insulator 124 and the endinsulator 122 may be integrally formed. For example, the wall insulator124 may be a tubular side wall of a cap insulator 2100, and the endinsulator 122 may be a flat end of the cap insulator. The cap insulator2100 can have the shape that results from combining the wall insulator124 with the end insulator 122. More particularly, the cap insulator2100 can be formed by joining an outer edge 802 of the end insulator 122to the distal wall end 206 or the proximal wall end 208 of the wallinsulator 124. The edges can be joined, e.g., by a thermal or adhesivewelding process. Alternatively, the cap insulator 2100 can be formed ina molding or thermoforming process, in which the end insulator 122 andwall insulator 124 portions are integrally fabricated. Similarly, slots804 can be formed, during or after the molding or thermoforming process,as holes in the end of the insulating cup to permit passage ofelectrical pins.

It will be appreciated that the cap insulator 2100 can be placed overthe flexible circuit assembly 120 to constrain and isolate the flexiblecircuit assembly 120 from adjacent conductive components. Furthermore,several cups may be used to isolate the flexible circuit assembly 120 atboth ends. For example, a first cap insulator can be used to isolate aproximal portion of the flexible circuit assembly 120, and a second capinsulator can be used to isolate a distal portion of the flexiblecircuit assembly 120. The cap insulators can have walls sized to overlapeach other, e.g., in a sliding fit by sliding one cap wall into and overanother. The cap insulators may also have holes sized to receive batterypins (in the case of the proximal cap insulator) or a feedthrough pin(in the case of the distal cap insulator. Accordingly, the capinsulators can be assembled onto each other to completely encapsulatethe flexible circuit assembly 120 within an insulated cavity surroundedby the cap insulator walls and ends.

Based on the assembled structure described above, it will be appreciatedthat the individual components of the electrical feedthrough assemblycan be fit together during assembly, e.g., during a method ofmanufacturing the biostimulator 100. The method can include a sequenceof operations. The operations are described below in one order, whichmay be suitable for the flexible circuit assembly 120 having socketconnectors to connect to external electrical pins. In an alternativeembodiment, such as when the flexible circuit assembly 120 hasmetallized pads to connect to the external electrical pins, theoperations may be performed in an alternative order.

In an operation, the flexible circuit assembly 120 can be folded alongthe fold region 316 into the stacked configuration 702. In the stackedconfiguration 702, the first mounting region 312 faces the secondmounting region 314 in the transverse direction 325. The foam tape mayoptionally be placed between the mounting region faces prior to foldingthe flexible circuit assembly 120, and thus, may temporarily hold theflexible circuit assembly 120 in the stacked configuration 702 duringthe assembly process.

In an operation, the battery pins 902 can be inserted through respectiveslots 804 in the end insulator 122. Accordingly, the battery pins 902can extend distally to pin tips that are separated from the distal face904 of the battery by the end insulator 122.

In an operation, the battery pins 902 of the battery can be insertedinto respective battery connectors 410 on the folded mounting surface306. When the folded flexible circuit assembly 120 is loaded onto thebattery pins 902, the longitudinal edges of the flexible substrate 304can be at a same longitudinal location, and can be separated from thedistal face 904 of the battery by the end insulator 122. Accordingly,the protective gap 704 within the interior of the folded flexiblecircuit assembly 120 can contain the battery pins 902 and can beseparated from the battery by the end insulator 122.

In an operation, the wall insulator 124 can be disposed over and aroundthe folded flexible circuit assembly 120. The housing 102 can be loadedover the wall insulator 124 and mounted on the battery such that theinner surface 118 of the housing 102 extends around the wall insulator124 and the flexible circuit assembly 120. The peripheral edge 1204 ofthe flexible circuit assembly 120 can physically contact an interiorsurface of the wall insulator 124, and can press the wall insulator 124radially outward into contact with the inner surface 118 of the housing102. Accordingly, the housing 102 can provide an external support to theflexible circuit assembly 120.

In an operation, the feedthrough pin 1104 is inserted through theaperture 326 in the fold region 316 of the flexible circuit assembly120. The feedthrough pin 1104 can engage the feedthrough connector 402,e.g., can insert into the socket connector, on the mounting surface 306such that the feedthrough pin 1104 extends from a tip within theprotected gap to a base outside of the protected gap. The fold region316 of the flexible substrate 304 can separate the protected gap fromthe distal region of the electronics compartment 116. The battery can behermetically sealed to the proximal end of the housing 102 by a firstcircumferential weld, and the header assembly 110 can be hermeticallysealed to the distal end of the housing 102 by a second circumferentialweld. The assembled biostimulator 100 can then be delivered andimplanted at a target site to deliver pacing impulses to the targetsite.

FIGS. 13-16 illustrate assembly of the biostimulator 100, and moreparticularly, illustrate the assembly of the biostimulator 100 havingflexible circuit assembly 120 that includes metallized pads 1302 toconnect to the feedthrough pin 1104 and battery pins 902. It will beappreciated that the assembly operations described below may beperformed in any order. For example, whereas the housing 102 may beloaded over the flexible circuit assembly 120 after the feedthrough pin1104 is attached to the metallized pad 1302 in the followingdescription, it will be appreciated that the housing 102 may be loadedover the flexible circuit assembly 120 before the feedthrough pin 1104is attached to the socket connector in the embodiments described above.

Referring to FIG. 13, a cross-sectional view of a header assemblyconnected to a flexible circuit assembly is shown in accordance with anembodiment. In an embodiment, the feedthrough connector 402 and thebattery connectors 410 are metallized pads 1302. For example, the padscan be formed on the flexible substrate 304 using semiconductorfabrication processes. The flexible circuit assembly 120 can be foldedalong the fold region 316 into the stacked configuration 702.

In an embodiment, the aperture axis 352 can extend between the firstmounting region 312 and the second mounting region 314, e.g., over themetallized pads 1302, when the flexible circuit assembly 120 is in thestacked configuration 702. For example, the aperture axis 352 can extendparallel to the longitudinal axis 108, and in alignment with thefeedthrough connector 402. More particularly, the aperture axis 352 canbe between and laterally aligned with the feedthrough connector 402 andthe electronic component 310 when the flexible circuit assembly 120 isin the stacked configuration 702. When laterally aligned, a transverseplane containing the aperture axis 352 and extending in the transversedirection 325 can intersect the feedthrough connector 402. Accordingly,the feedthrough pin 1104 can extend through the aperture 326 and overthe feedthrough connector 402 to be placed in contact with metallizedpad 1302.

In an embodiment, the feedthrough pin 1104 is spot welded to themetallized pad 1302 of the feedthrough connector 402. Alternatively, thepin can be soldered to the pad. The feedthrough pin 1104 may be shorterwhen the electrical connectors 308 are metallized pads 1302, as comparedto when the electrical connectors 308 are socket connectors, because thespot weld, which requires minimal space, can connect the feedthrough pin1104 to the feedthrough connector 402. The feedthrough pin 1104 can beconnected to the feedthrough connector 402 prior to connecting thebattery pins 902 to the battery connectors 410. For example, thefeedthrough pin 1104 can be welded or soldered to the metallized pad1302.

Referring to FIG. 14, a cross-sectional view of a header assembly and abattery connected to a flexible circuit assembly is shown in accordancewith an embodiment. The battery pins 902 can be placed on correspondingmetallized pads 1302 of the flexible circuit assembly 120. For example,the battery pins 902 can be inserted through respective slots 804 in theend insulator 122, and placed onto or into the battery connectors 410.The battery pins 902 can be connected to respective battery connectors410 by respective spot welds. Alternatively, the pins may be soldered tothe pads. When the battery pins 902 are attached to the respectivebattery connectors 410, either by a thermal weld or by inserting thepins into a spring connector as described above, the end insulator 122can be retained between the flexible circuit assembly 120 and the distalface 904 of the battery.

Several advantages accrue from the use of the metallized pads 1302, orsimilar electrical connections using welded or solder construction totransmit power between the flexible circuit assembly 120 and externalcomponents, such as the energy source 107 (battery). As described above,the metallized pads 1302 use less space than socket connectors, andthus, can reduce an overall size of the biostimulator 100. Second, weldattachments can be produced at lower cost than other connectors, such assocket connectors. Third, weld attachments can be easily validated,which can improve manufacturability and contribute to long termreliability of the biostimulator 100.

In an embodiment, after the feedthrough pin 1104 is connected to thefeedthrough connector 402 and the battery pins 902 are connected to thebattery connectors 410, the double-sided foam tape 1202 can be disposedbetween the mounting surface 306. The flexible circuit assembly 120 canthen be folded to press the mounting surface 306 against the foam tape1202. Accordingly, the foam tape 1202 can hold the flexible circuitassembly 120 in the folded, or stacked, configuration.

Referring to FIG. 15, a cross-sectional view of an electronicscompartment of a biostimulator containing a wall insulator and aflexible circuit assembly is shown in accordance with an embodiment. Inan operation, the wall insulator 124 can be mounted over the stackedflexible circuit assembly 120. For example, the wall insulator 124 canbe slid over the flange 1004 until the proximal wall end 208 contactsthe end insulator 122 and/or the distal face 904 of the battery. Whenthe wall insulator 124 is placed over the flange 1004, the distal wallend 206 can be adjacent to a proximal edge of the flange 1004, and thus,the wall insulator 124 can extend around the flexible circuit assembly120. More particularly, the flexible circuit assembly 120 can containthe flexible circuit assembly 120 having electrical connectors 308connected to the feedthrough 1102 and the battery.

After sliding the wall insulator 124 over the flexible circuit assembly120, the housing 102 can be added over the wall insulator 124. Moreparticularly, the housing 102 can be assembled over the folded flexiblecircuit assembly 120 to isolate and contain the electrical components.The housing 102 can slide over the flange 1004 until a proximal end ofthe housing 102 abuts the battery. A distal end of the housing 102, bycontrast, is adjacent to the flange 1004. Accordingly, when the housing102 is mounted on the battery, the inner surface 118 can extend aroundthe end insulator 122, the wall insulator 124, and the flexible circuitassembly 120.

The biostimulator 100 assembly can be secured by attaching the headerassembly 110, e.g., the flange 1004, to the housing 102, and byattaching the housing 102 to the battery. In an embodiment, a firstcircumferential weld 1502 is formed along a seam between the flange 1004and the distal end of the housing 102. Similarly, a secondcircumferential weld 1504 can be formed along a seam between the housing102 and the battery. The circumferential welds secure and seal thecomponents. More particularly, the welds can be hermetic welds thatisolate the components within the electronics compartment 116 from asurrounding environment.

In an embodiment, when the housing 102 and the wall insulator 124 aresecured around the flexible circuit assembly 120, the components aretightly fit together. The peripheral edges 1204 can deflect outward,e.g., when the foam tape 1202 loses grip, and press outward against theinterior surface of the wall insulator 124. In the case of thecorrugated wall insulator 124, the wall insulator 124 can expand outwardand press against the inner surface 118 of the housing 102. Accordingly,the wall insulator 124 may be sandwiched between the inner surface 118of the housing 102 and the peripheral edges 1204 of the flexible circuitassembly 120.

In an embodiment, one or more of the end insulator 122 or the wallinsulator 124 include an adhesive film (not shown). The adhesive filmcan include a pressure-sensitive or other adhesive covering one or moreof the surfaces of the end insulator 122 or the wall insulator 124. Forexample, an interior surface of the wall insulator 124 and an uppersurface of the end insulator 122 may include adhesive. Accordingly, thesurfaces facing the flexible circuit assembly 120 can have adhesive, andthus, the adhesive film(s) can attach the insulators 122, 124 to theflexible circuit assembly 120. In the embodiments described above, theuse of adhesive to bind the components within housing 102 to each othercan facilitate several advantages. First, the adhesive can improveplacement by reducing the likelihood that components will shift withinthe housing 102. Second, by the adhesive can ensure insulation of theelectrical components. For example, by reducing the likelihood ofshifting of the electronic components, formation of a gap between theinsulators 122, 124 may be prevented, thereby reducing the likelihoodthat the electronic components of the flexible circuit assembly 120could become exposed to an interior surface of the conductive housing102.

Referring to FIG. 16, a perspective view of an electronics compartmentof a biostimulator containing a wall insulator overmolded on a flexiblecircuit assembly is shown in accordance with an embodiment. The wallinsulator 124 may be overmolded onto the flexible circuit assembly 120.The overmolding operation may occur, for example, after the feedthroughpin 1104 and the battery pins 902 are connected to respective electricalconnectors 308 on the flexible circuit assembly 120. An overmold 1602may be placed over and around the components of the folded flexiblecircuit assembly 120. The overmold 1602 can be a polymer material, forexample, and can isolate and electrically insulate the components fromthe housing 102. More particularly, when the housing 102 is loaded overthe overmolded wall insulator 124, the overmold 1602 material canseparate the electrical connectors 308 of the flexible circuit assembly120 from the inner surface 118 of the housing 102 (not shown). Theovermolded wall insulator 124, therefore, serves essentially the samefunction as the tubular insulating sleeve described above. The overmold1602 can be hermetically sealed within the electronics compartment 116by forming circumferential welds around the housing 102 at the flange1004 and the battery, as described above.

Referring to FIG. 17, a cutaway view of a moisture getter in anelectronics compartment of a biostimulator is shown in accordance withan embodiment. The electronics compartment 116 can be hermeticallysealed within the biostimulator 100. For example, the header assembly110 can be joined to a distal end of the housing 102 (not shown) by ahermetic weld around a circumference of the distal end. Similarly, thebattery can be joined to a proximal end of the housing 102 (not shown)by hermetic weld around a circumference of the proximal end.Accordingly, any moisture trapped within the electronics compartment 116during the manufacturing process may remain there unless steps are takento eliminate the moisture.

In an embodiment, the biostimulator 100 includes a moisture getter 1702within the electronics compartment 116. The moisture getter 1702 can bea desiccant that absorbs residual moisture within the electronicscompartment 116. The moisture getter 1702 can include the desiccantwithin a permeable matrix, such as a polymer. An example of a suitabledesiccant material includes zeolite, however, other desiccants may beused in the moisture getter 1702.

The moisture getter 1702 can be loaded into and retained by the getterholder 1704. The getter holder 1704 can be mounted on a component withinthe electronics compartment 116, such as on a proximal face or surfaceof the header assembly 110. The getter holder 1704 can occupy spacewithin the electronics compartment 116 without interfering with thecomponents of the flexible circuit assembly 120.

Referring to FIG. 18, a perspective view of a moisture getter holder isshown in accordance with an embodiment. The getter holder 1704 caninclude a cavity 1802. For example, the cavity 1802 can be a recessmachined or otherwise formed in a surface of the getter holder 1704 toallow sufficient moisture getter 1702 to be loaded within the cavity1802 to scavenge moisture from the electronics compartment 116. In anembodiment, the cavity 1802 has a volume of 1.5-2.5 mm³, e.g., 1.9 mm³,to contain a corresponding volume of moisture getter material. Themoisture getter 1702 can be loaded, e.g., injected, into the cavity1802. In an embodiment, the cavity 1802 has an opening that facesproximally within the electronics compartment 116. For example, thegetter holder 1704 can be fastened to the header assembly 110 such thatthe opening of the cavity 1802 faces toward the battery. Alternatively,the getter holder 1704 can be mounted in a proximal region of theelectronics compartment 116, and the opening of the cavity 1802 can facetoward the header assembly 110.

In an embodiment, the getter holder 1704 is fabricated from a lowmoisture material. For example, the getter holder 1704 can be machinedfrom a glass-reinforced epoxy laminate material. Alternatively, thegetter holder 1704 can be molded from a thermoset polymer, a ceramicmaterial, or other low moisture materials.

Referring to FIG. 19, a perspective view of a moisture getter in anelectronics compartment of a biostimulator is shown in accordance withan embodiment. Rather than being a separate component, the getter holder1704 can be integrated with another component of the biostimulator 100.For example, the getter holder 1704 can be fastened to or integrallyformed with the end insulator 122. In an embodiment, the getter holder1704 is bonded to a distal face of the end insulator 122, and theopening of the cavity 1802 containing the moisture getter 1702 can facein the distal direction toward the header assembly 110.

Referring to FIG. 20, a perspective view of a moisture getter holder isshown in accordance with an embodiment. The getter holder 1704 may beintegrally formed with the end insulator 122. For example, the endinsulator 122 may have a planar proximal face and a non-planar distalface. Rather than having a planar distal face, the getter holder 1704can be a trough that extends from the distal face 904. The integrallyformed end insulator 122 can separate the battery from the flexiblecircuit assembly 120, and can hold the moisture getter 1702. Asdescribed above, the integrally formed end insulator 122 can includeslots 804 to receive the battery pins 902. In an embodiment, the getterholder portion of the end insulator 122 and the flat portion of the endinsulator 122 having the slots 804 can be formed from a glass-reinforcedepoxy laminate material, or another material having low moisture andelectrically insulating properties. Accordingly, the end insulator 122can facilitate scavenging moisture from the electronics compartment 116and can reduce a likelihood of electrical short-circuiting between theflexible circuit assembly components and other biostimulator components.

Alternative insulating structures used to isolate the flexible circuitassembly 120 from the housing 102 are contemplated within the scope ofthis description. Referring to FIG. 22, a perspective view of aninsulating shroud is shown in accordance with an embodiment. Aninsulating shroud 2200 can be an insulator, e.g., a thin sheet ofpolyimide or another insulating material, having one or more foldablesections 2202. The foldable sections 2202 can be rectangular, orother-shaped, sections that are joined along respective fold lines(dotted lines). In an embodiment, the foldable sections 2202 foldrelative to each other to wrap around the flexible circuit assembly 120and to isolate the electronic components from surrounding structures.For example, a first fold section 2202 a can be apposed to the firstmounting region 312 during assembly, when the flexible circuit assembly120 is in a folded configuration. One or more additional fold sections,such as a top fold section 2202 b and/or a bottom fold section 2202 ccan then be folded along respective fold lines to cause the wings towrap over a top end and a bottom end of the folded circuit assembly, andto appose the second mounting region 314. Optionally, one or more sidefold sections 2202 d can then be folded along respective fold lines tocause the wings to wrap around the sides of the folded circuit assembly.Accordingly, the wings of the insulating shroud 2200 can fold around theelectronic components to encapsulate the flexible circuit assembly 120and isolate the electronic components from the housing 102. The slots804 can be formed in the insulating shroud 2200 to receive a feedthroughpin or battery pins. The slots 804 can be located in the insulatingsheet of material along the fold lines that distinguish the first foldsection 2202 a from an adjacent fold section.

Several embodiments, which have been described above, are summarized inthe following paragraphs. In an embodiment, a flexible circuit assemblyfor a biostimulator includes a flexible substrate. The flexiblesubstrate includes a mounting surface having a fold region between afirst mounting region and a second mounting region. The flexiblesubstrate is configured to fold along the fold region into a stackedconfiguration such that the first mounting region faces the secondmounting region. The flexible substrate includes an aperture in the foldregion having an aperture axis.

The flexible circuit assembly may include a feedthrough connector on themounting surface. When the flexible substrate is in the stackedconfiguration the aperture axis can extend between the first mountingregion and the second mounting region in alignment with the feedthroughconnector. The flexible circuit assembly may include an electroniccomponent on the mounting surface.

The feedthrough connector may be on the first mounting region and theelectronic component may be on the second mounting region.

The aperture may be centered on the mounting surface.

The flexible circuit assembly may include several battery connectors onthe mounting surface.

The feedthrough connector and the several battery connectors may besocket connectors having respective socket axes extending parallel toeach other. The socket axis of the feedthrough connector may belaterally between the socket axes of the battery connectors. Thefeedthrough connector and the several battery connectors may bemetallized pads.

In an embodiment, a biostimulator includes a housing having an innersurface extending around an electronics compartment. The biostimulatorincludes a flexible circuit assembly within the electronics compartment.The flexible circuit assembly includes a flexible substrate including amounting surface having a fold region between a first mounting regionand a second mounting region. The flexible substrate is folded along thefold region such that the first mounting region faces the secondmounting region. The flexible substrate includes an aperture in the foldregion. The aperture has an aperture axis. The flexible circuit assemblyincludes a feedthrough connector on the mounting surface. The apertureaxis extends in alignment with the feedthrough connector. The flexiblecircuit assembly includes an electronic component on the mountingsurface.

The feedthrough connector may be on the first mounting region and theelectronic component may be on the second mounting region such that thefeedthrough connector and the electronic component are in a stackedconfiguration.

The aperture may be centered on the mounting surface.

The biostimulator may include a foam tape between the feedthroughconnector and the electronic component.

The biostimulator may include a battery having several battery pinsextending from a distal face in a longitudinal direction. The flexiblecircuit assembly includes several battery connectors connected torespective battery pins of the battery. The battery pins have respectivepin axes extending parallel to the aperture axis of the aperture. Thebiostimulator may include an end insulator between the distal face ofthe battery and the flexible circuit assembly. The end insulator may beplanar and may include several slots. The several battery pins mayextend through the several slots into the electronics compartment. Theend insulator may have an outer edge. The outer edge and the innersurface of the housing may have a same profile.

The biostimulator may include a wall insulator extending around theflexible circuit assembly within the electronics compartment.

The biostimulator may include a moisture getter within the electronicscompartment.

In an embodiment, a method includes folding a flexible circuit assemblyalong a fold region into a stacked configuration. The flexible circuitassembly includes a mounting surface having the fold region between afirst mounting region and a second mounting region. The first mountingregion faces the second mounting region in a transverse direction whenthe flexible circuit assembly is in the stacked configuration. Themethod includes connecting a feedthrough pin to a feedthrough connectoron the mounting surface between the first mounting region and the secondmounting region. The feedthrough pin extends through an aperture in thefold region. The method includes connecting several battery pins of abattery to respective battery connectors on the mounting surface.

The method may include inserting the several battery pins throughrespective slots in an end insulator. The end insulator may be betweenthe battery and the flexible circuit assembly when the several batterypins are attached to the respective battery connectors. The method mayinclude mounting a wall insulator over the stacked flexible circuitassembly such that the wall insulator extends around the flexiblecircuit assembly. The method may include mounting a housing on thebattery such that an inner surface of the housing extends around the endinsulator, the wall insulator, and the flexible circuit assembly. Thewall insulator may be sandwiched between the inner surface of thehousing and peripheral edges of the flexible circuit assembly. Themethod may include attaching the housing to a header assembly and thebattery to contain an electronics compartment between the battery, theinner surface of the housing, and the header assembly. The flexiblecircuit assembly may be within the electronics compartment. The headerassembly may include a feedthrough having the feedthrough pin, anelectrode tip, and a fixation element.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

1. A biostimulator, comprising: a housing having an electronicscompartment; a flexible circuit assembly within the electronicscompartment, wherein the flexible circuit assembly includes a pluralityof battery connectors; a battery having a plurality of battery pinsextending from a distal face; and an end insulator between the distalface of the battery and the flexible circuit assembly, wherein the endinsulator includes a plurality of slots, and wherein the plurality ofbattery pins extend through the plurality of slots into the electronicscompartment to connect to the plurality of battery connectors.
 2. Thebiostimulator of claim 1, wherein the end insulator is planar.
 3. Thebiostimulator of claim 1, wherein one or more of the plurality of slotshas an elliptical profile.
 4. The biostimulator of claim 1, wherein afirst slot of the plurality of slots has a larger dimension than asecond slot of the plurality of slots.
 5. The biostimulator of claim 1,wherein an inner surface of the housing extends around the end insulatorand the flexible circuit assembly.
 6. The biostimulator of claim 5,wherein the end insulator has an outer edge, and wherein the outer edgeand the inner surface of the housing have a same profile.
 7. Thebiostimulator of claim 6, wherein an outer diameter of the outer edge iswithin 10% of an inner diameter of the inner surface.
 8. Thebiostimulator of claim 1, wherein the end insulator includes adielectric film.
 9. The biostimulator of claim 1, wherein the endinsulator includes a getter holder, and further comprising a moisturegetter in a cavity of the getter holder.
 10. The biostimulator of claim1, wherein the end insulator is a fold section of an insulating shroudhaving foldable sections, and wherein the foldable sections wrap overthe flexible circuit assembly.
 11. The biostimulator of claim 1, whereinthe flexible substrate includes a mounting surface having a fold regionbetween a first mounting region and a second mounting region, whereinthe flexible substrate is configured to fold along the fold region intoa stacked configuration so that the first mounting region faces thesecond mounting region, and wherein the flexible substrate includes anaperture in the fold region.
 12. The biostimulator of claim 11 furthercomprising a processor and a feedthrough connector on the mountingsurface, wherein the processor is configured to control generation of apacing impulse, and wherein the feedthrough connector is configured toreceive the pacing impulse and to transmit the pacing impulse throughthe aperture to a target tissue.
 13. The biostimulator of claim 1further comprising a header assembly mounted on the housing such thatthe flexible circuit assembly is enclosed between the header assembly,the housing, and the battery.
 14. A method, comprising: inserting aplurality of battery pins of a battery through a plurality of slots ofan end insulator; and connecting a plurality of battery connectors of aflexible circuit assembly to the plurality of battery pins, wherein theend insulator is between a distal face of the battery and the flexiblecircuit assembly.
 15. The method of claim 14, wherein the end insulatoris planar.
 16. The method of claim 14, wherein one or more of theplurality of slots has an elliptical profile.
 17. The method of claim 14further comprising mounting a housing on the battery such that theflexible circuit assembly is within an electronic compartment of thehousing.
 18. The method of claim 17, wherein an inner surface of thehousing extends around the end insulator and the flexible circuitassembly.
 19. The method of claim 17 further comprising mounting aheader assembly on the housing such that the flexible circuit assemblyis enclosed between the header assembly, the housing, and the battery.20. The method of claim 14 further comprising folding the flexiblecircuit assembly along a fold region into a stacked configuration,wherein the flexible circuit assembly includes a mounting surface havingthe fold region between a first mounting region and a second mountingregion, and wherein the first mounting region faces the second mountingregion in a transverse direction when the flexible circuit assembly isin the stacked configuration.